Some archaea have unique phospholipids in their cytoplasmic membrane that

Archaea are known as the small single-celled microorganisms in a structure like bacteria. Archaea are living in an environment such as soil, and water where low oxygen is present and they are called obligate anaerobes.

The unique cytoplasmic structure of Archaea is made up of lipid bilayer or monolayers which is composed of diglycerol tetraethers. Archaea phospholipids layer lack fatty acid, and instead of fatty acids, they contain hydrocarbon derivative isoprene which is linked to the backbone of glycerol with the help of ether bonds.

if you add everything up correctly you should get 69 i got this because 50 plus 19 is it